1. Field of the Invention
The present invention relates to a heat sink with fins suitable for cooling heat generating components such as semiconductor chips or the like.
2. Related Art
When using electronic components such as semiconductor devices and the like mounted on electric/electronic components including CPUs of personal computers, laser light emitting diodes and power transistors, they inevitably generate heat to some extent. In these days, as an amount of heat generated by an electronic component becomes larger, it becomes a technical problem to cool it. Known as a typical method of cooling electric/electronic components which require cooling are a method of lowering a temperature of air inside the housing of a component, a method of directly cooling a component to be cooled by mounting a cooling body onto the component, and the like.
Used as cooling bodies to be mounted on components to be cooled are a plate member made of a material having excellent heat conductivity such as copper and aluminum, a flat-type heat pipe, a cylindrical heat pipe and the like. A flat-type heat pipe is a plate-type heat pipe. A cylindrical heat pipe is a round-bar-shaped heat pipe.
Next, brief description is made about heat pipes. A heat pipe is a container having a cavity, in which a working fluid is sealed. Since the cavity is vacuumized, the working fluid is easy to be vaporized.
Now, an operation of a heat pipe is briefly described. At a heat absorbing side of the heat pipe, a working fluid is vaporized by heat transferred in a material of a container of the heat pipe. The vaporized working fluid is moved to a heat dissipating side of the heat pipe. At the heat dissipating side, the vaporized working fluid is cooled to become liquid again. Then, the liquefied working fluid flows back to the heat absorbing side (circulation). Such phase transformation and movement of the working fluid allows heat to be moved.
Circulation of the working fluid is carried out by gravity or capillary force. For a gravity type heat pipe, a working fluid is circulated by arranging a heat absorbing portion of the heat pipe below a heat dissipating portion. For a heat pipe which utilizes capillary force in circulation of a working fluid, the working fluid is circulated by capillary force of a groove which is provided in an inner wall of the cavity, or by capillary force of a wick of metal mesh, porous structure or the like which is inserted in the cavity
Thus, in a heat pipe, a large amount of heat is transferred by phase transformation and moving of the working fluid in a hermetically sealed cavity of the heat pipe. Surely, some heat is transferred by a container of the heat pipe, however, its amount is relatively small.
In addition, used as a cooling body to be mounted on a component to be cooled is a heat sink having a base plate with heat dissipating fins. Typical heat dissipating fins include extruded fins of one-piece fins and base plate formed by way of an extrusion member, brazed fins formed by jointing heat dissipating fins to a base plate by brazing, crimped fins formed by jointing heat dissipating fins to a base plate by mechanical crimping and the like.
Crimped fins are formed as follows: a base plate is provided with a plurality of grooves, then, into which heat dissipating fins are inserted to be crimped from both sides.
A base plate and heat dissipating fins are made of a material having excellent heat conductivity, such as copper and aluminum.
Thus formed crimped fins have the following advantages. A small fin pitch is allowed, which can not be realized in extruded fins which are formed by way of a extrusion member. For brazing, since jointing is carried out at a high temperature, annealing occurs and the material is deteriorated, which results in poor straightness of the fins. For crimped fins, jointing can be performed at a low temperature with excellent fin straightness. Further, for crimped fins, a base plate and heat dissipating fins may be made of different metals. For example, a copper base plate and aluminum heat dissipating fins may be prepared to be jointed to each other.
However, when a heat sink is formed by jointing aluminum heat dissipating fins to an aluminum base plate by crimping, heat dissipating performance is limited, which presents a problem that a component to be cooled of high heat generating density can not be cooled enough. On the other hand, when a heat sink is formed by jointing aluminum heat dissipating fins to a copper base plate by crimping, heat dissipating performance is improved, however, there occurs a problem of heavy weight of the heat sink.
Accordingly, it is an object of the present invention to provide a light-weight heat sink with fins with a small fin pitch and excellent heat dissipating performance.